Multi-stage counter-current concentrating method

ABSTRACT

A system and method for concentrating aqueous beverages such as fruit juices, beer, wine, vinegar, tea, coffee, and the like in which a slurry of feed liquid and seed crystals is formed in a scraped surface heat exchanger of a first stage and supplied to a recrystallizer where larger crystals grow, the liquid in the recrystallizer being withdrawn with part recirculated to the heat exchanger of a succeeding stage. The slurry of larger crystals in the recrystallizer of the first stage is also withdrawn and the crystals separated in a wash column. The larger crystals grown in the second stage recrystallizer are supplied to the recrystallizer of the first stage where the seed crystals melt and reform on the larger crystals and the larger crystals from the third stage are similarly supplied to the recrystallizer of the second stage.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a system and method for concentrating anaqueous beverage.

Concentrating aqueous beverages for storage, transportation and sale hasa number of substantial advantages and is being used more and morewidely for an increasing variety of beverages. For some products, forexample, coffee and tea, the purpose of concentration is to produce aproduct which is convenient for the consumer to use. For other productssuch as wine, milk, beer, vinegar and the like, the greatest advantagemay lie in reducing the bulk of the material and thus reducing theexpense of storage and transportation.

Concentration of such aqueous beverages can be done in one of threeways--evaporation, freeze concentration, or reverse osmosis. Inevaporation techniques the beverage is heated or steam is passedtherethrough to remove the water by evaporation. In freeze concentrationtechniques, a slurry of ice is formed in the beverage and the ice thenseparated from the resulting concentrated liquor. One of the drawbacksto evaporation techniques is that many of the subtle flavor componentsof aqueous beverages are volatile and escape during evaporation. Thisdifficulty can in part be overcome by stripping many of those componentsbefore evaporation and then returning them to the concentrated beverage.However, some degradation in flavor seems to be inevitable withevaporation techniques. Reverse osmosis is non-selective and flavorcomponents are lost making it unsatisfactory for concentration ofaqueous beverages.

Freeze concentrated products do not suffer from degradation sinceretention of flavor components is almost one hundred percent. The maindrawbacks in the past to freeze concentration processes have beenexpense and insufficient volume of operation.

The present invention relates to a process and system for freezeconcentration which is more efficient than previous techniques and whichcan process large volumes of concentrated aqueous beverages inrelatively short times.

The patent to Thijssen et al U.S. Pat. No. 4,004,886 describes a processand apparatus for crystallization in which a slurry of seed ice crystalsand mother liquor are produced in a scraped surface heat exchanger andcontinuously supplied to a recrystallization vessel in which thecrystals grow. The mother liquor in the recrystallizer vessel iscontinuously mixed and recirculated to the scraped surface heatexchanger via a filter which prevents crystals from leaving therecrystallizer. Almost all of the crystals in the recrystallizer meltand reform on a few small seed crystals to produce a crystal slurryhaving relatively uniform sized crystals therein, which slurry isremoved continuously from the recrystallizer as a crystal suspension. Inthis arrangement, the residence time in the system is substantiallyreduced because of the melting of the seed crystals supplied to therecrystallizer from the heat exchanger and reformation of these meltedcrystals onto the few large crystals which then grow as spheres. Whileothers in the past have proposed systems using both scraped surface heatexchangers and larger tanks in which crystal growth takes place, forexample, the patent to Walker U.S. Pat. No. 3,156,571, it is the meltingof the vast majority of the ice crystals and the recirculation only ofliquid from the recrystallizer which reduces the residence time andproduces the uniform crystal size in both the system described in theThijssen et al patent, and the present invention. The uniform crystalsize in particular permits use of wash columns in the system instead ofcentrifuge or other separating devices which have technical and otherdisadvantages.

The slurry which is removed from the recrystallizer in theabove-described system of the Thijssen et al patent is preferablysupplied to a wash column, for example, as described in the ThijssenU.S. Pat. No. 3,872,009. In this particular wash column, the slurry issupplied to the bottom of a column and then compacted against the icemass by a piston which periodically pushes the mass upward. The ice atthe top of the column is chopped and removed from the column where it ismelted and at least in part returned to the column to flow downward whenthe piston applies pressure to the bottom of the column to maintain awash front. The mother liquor is removed as concentrated liquor throughperforations in the piston.

In the system of the present invention, a plurality of concentratingunits are connected together for counter-current operation.Countercurrent freeze concentration as such is not new. For example,Ganiaris U.S. Pat. No. 3,283,522 describes a multi-stage freezeconcentrating system in which ice passes toward the first stage andmother liquor toward the last stage. However, in the present invention,only the crystals from the succeeding stage grow; in all stages exceptthe last, practically all seed crystals (of the order of 99% and atleast more than 90%) formed in that stage melt and reform on the largercrystals from the succeeding stages and this remarkably improves theefficiency of concentration. Further, the separation is done in thelowest concentration step where viscosity is lowest and the wash columnperforms most efficiently.

In the first stage of the present invention which receives the feedliquid to be concentrated and produces a first intermediate concentratedsolution, a slurry of ice crystals and liquid in a recrystallizationvessel are supplied to a separator such as a wash column and theintermediate concentrated solution is passed to a second stage. The icecrystals from the second stage are passed countercurrent to thedirection of movement of the aqueous beverage liquid and supplied to therecrystallization vessel of the first stage. Almost all of the seedcrystals produced in the first stage, for example, by a scraped surfaceheat exchanger, then melt and reform upon the larger crystals suppliedfrom the second stage. Third and additional stages can also be provided,each passing at least the ice back directly to the recrystallizationvessel of the preceding stage so that the crystalline growth takes placeonly on the crystals which are supplied from the succeeding stage andpractically all of the crystals generated in each stage except the lastmelt and reform thereon.

By utilizing this countercurrent approach, three stages which each canremove 250 kilograms of ice per hour from a liquid feed will remove atleast 1800 kilograms per hour in a countercurrent configuration, asopposed to 750 kilograms per hour in parallel operation and 1200kilograms per hour in serial operation in which only the liquid ispassed through succeeding stages.

The water removal capacity in kilograms of ice per hour of any freezeconcentration system depends on the viscosity of a given productconcentration and the diameter of the ice crystals at thatconcentration. The viscosity of any liquid is strongly dependent uponits concentration. The crystal growth velocity is dependent also uponconcentration so that an increase in concentration results in a sharpdecrease of the crystal growth velocity and an increase in viscosity,both of which substantially reduce the rate of crystal growth. Using thecountercurrent approach, crystal growth can take place on crystals whichhave already grown large and can take place in a less concentratedsolution, both factors decreasing residence time and hence increasingcapacity. Separation in the lowest concentration stage is also mostefficient.

Other purposes and objects of the invention will be clear from thefollowing detailed description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of a first embodiment of thecounter-current system of the present invention;

FIG. 2 shows a sectional view of a first separator according to thefirst embodiment;

FIG. 3 shows a schematic view of the pneumatic control system foroperating the separator of FIG. 2;

FIG. 4 shows a front view of the filter from the separator of FIG. 2;

FIG. 5 shows a sectional view of a second separator according to thefirst embodiment;

FIG. 6 shows a schematic diagram of a second embodiment of thecounter-current system of the present invention;

FIG. 7 shows a sectional view of a first separator according to thesecond embodiment;

FIG. 8 shows a sectional view of a second separator according to thesecond embodiment.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference is now made to FIG. 1 which illustrates in schematic form acounter-current crystallization plant comprising three concentratingstages generally indicated as 20, 22 and 24. It will be understood thatthe present invention can be utilized with as few as two stages and asmany as are necessary and appropriate to achieve desired concentration.An aqueous beverage liquid to be concentrated is supplied to a retainingtank 26 of stage 20 continuously or periodically. Feed liquid to tank 26is supplied by pump 30. A portion of the liquid in recrystallizingvessel 32 is removed via filter 34 as described in the above-mentionedThijssen U.S. Pat. No. 4,004,886, the disclosure of which is herebyincorporated by reference. A part of the liquid removed from vessel 32as a first intermediate concentrated liquid and the feed liquor fromtank 26 are mixed and supplied to three parallel connected conventionalscraped surface heat exchangers 36, 37 and 38 by pumps 40, 41 and 42. Itis preferred to use two or three scraped surface heat exchangers inparallel in each stage rather than a large one so that if one shouldmalfunction, the system can still continue in operation. As described inthe above-mentioned Thijssen U.S. Pat. No. 4,044,886, the slurry of seedcrystals and liquid formed as output of the scraped surface heatexchangers is supplied to vessel 32. These seed crystals preferably havean effective diameter less than 5-10 microns. The seed crystalspractically all melt within vessel 32 and reform on larger crystals fromthe succeeding stage supplied as described below. The slurry of largerice crystals and liquid in vessel 32 is removed therefrom and the iceseparated from the mother liquor in wash column 50 as described in theabove-mentioned patent to Thijssen U.S. Pat. No. 3,872,009, thedisclosure of which is also hereby incorporated by reference. The meltedice is removed by wash column 50 from the system as water and discarded.The concentrated output of wash column 50 is supplied to feed tank 26and hence to the scraped surface heat exchangers as described above.

A portion of the liquid in recrystallizing vessel 74 is removed viafilter 76 as described in the above mentioned Thijssen U.S. Pat. No.4,004,886, the disclosure of which is hereby incorporated by reference.A part of the liquid removed from vessel 74 as a second intermediateconcentrated liquid and the other part of the first intermediateconcentrated liquid removed from vessel 32 via filter 34 is mixed andsupplied to two parallel connected conventional scraped surface heatexchangers 70 and 72 by pumps 66 and 68. It is preferred to use twoscraped surface heat exchangers in parallel in each stage rather than alarge one, so that if one should malfunction, the system can stillcontinue in operation. As described in the above mentioned Thijssen U.S.Pat. No. 4,044,886 the slurry of seed crystals and liquid formed asoutput of the scraped surface heat exchangers is supplied to vessel 74.These seed crystals preferably have an effective diameter less than 5-10microns. The seed crystals practically all melt within vessel 74 andreform on larger crystals from the succeeding stage supplied asdescribed below. The slurry of ice crystals and liquid in recrystallizer74 is removed therefrom and the liquid partially separated by aseparator 82 and preferably mixed with the intermediate concentratedliquid from stage 20. The remainder of the liquid with ice crystals isfed to recrystallization vessel 32 where the relatively large icecrystals (compared to the crystals supplied by heat exchangers 36, 37and 38) grow as the seed crystals from heat exchangers 36, 37 and 38melt and reform on the larger crystals from stage 22.

A portion of the liquid in recrystallizing vessel 90 is removed viafilter 92 as described in the above mentioned Thijssen U.S. Pat. No.4,004,886, the disclosure of which is hereby incorporated by reference.A part of the liquid removed from vessel 90 as a final concentratedliquid and the other part of the second intermediate concentrated liquidremoved from vessel 74 via filter 76 is mixed and supplied to twoparallel connected conventional scraped surface heat exchangers 86 and87 by pumps 88 and 89.

It is preferred to use two scraped surface heat exchangers in parallelin each stage rather than a large one, so that if one shouldmalfunction, the system can still continue in operation. As described inthe above mentioned Thijssen U.S. Pat. No. 4,044,886 the slurry of seedcrystals and liquid formed as output of the scraped surface heatexchangers is supplied to vessel 90. These seed crystals preferably havean effective diameter less than 5-10 microns. Most of the seed crystalssupplied by heat exchangers 86 and 87 melt in recrystallizing vessel 90and reform on those few crystals which do not melt. The slurry of icecrystals and liquid in recrystallizer vessel 90 is removed therefrom andthe liquid partially separated by a separator 100 and preferably mixedwith the intermediate concentrated liquid from stage 22. The remainderof the liquid with ice crystals is fed to recrystallization vessel 74where the relatively large ice crystals (compared to the crystalssupplied by heat exchangers 70 and 72) grow as the seed crystals fromheat exchangers 70 and 72 melt and reform on the larger crystals fromstage 24. The other part of the final concentrated liquid removed fromvessel 90 is removed from the system as product.

Reference is now made to FIG. 2 which shows a separator 100 for use inthe first embodiment diagrammatically illustrated in FIG. 1. Separator82 preferably is identical to separator 100. Separator 100 includes avessel 102 having an interior space 104 in which a piston 106 isreciprocated by conventional air cylinder 108. When the piston iswithdrawn, the slurry enters space 104 via inlet 110. Air cylinder 108is then operated to advance piston 106 and its cylindrical plastic faceplate 111 toward outlet 112, compacting the ice slurry. The liquid mixedwith the slurry is forced through filter 114 and outlet 116, andreturned to the stage from which it was withdrawn. After a suitableamount of liquid has been withdrawn leaving the slurry still liquidenough to move through outlet 112, a valve associated with outlet 112 isoperated to cause the slurry to be passed to the preceding stage asgenerally described above. Piston 106 advances to a position slightlybeyond filter 114, to scrape filter 114.

FIG. 3 shows the control circuit for operating pneumatic air cylinder106. Three microswitches 120, 122 and 124 are successively operated asthe cylinder 106 advances toward outlet 112. As piston 106 is withdrawn,valve 134 is open so that slurry is drawn into space 104. When switch120 is operated logic 132 closes valve 134, operating switch 129.Operation of switch 129 operates logic 126 to reverse the direction ofmovement of piston 106 which now advances to squeeze liquid from theslurry in space 104. When switch 122 is operated, logic 128 closes valve130 and logic 136 opens valve 138 so that the slurry is now pushed outoutlet 112. Operation of switch 124 causes logic 136 to close valve 138and operate switch 125. Operation of switch 125 causes logic 132 to openvalve 134 in turn operating switch 127. Operation of switch 127 operateslogic 126 to withdraw piston 106. The positions of switche 122determines the amount of liquid squeezed from the compacting ice mass.

FIG. 4 shows a view of the cylindrical filter which finds particular usein a separator as in this embodiment, and in the embodiments whichfollow. Such filters are well known in the art and used for a variety ofpurposes. A plurality of triangular shaped wires 156 are each fixed bywelding or otherwise at the point of the triangle to a plurality ofencircling bands 158. Wires 156 thus form slots through which the liquidcan move but from which the ice is excluded. As piston face 111 movespast filter 114, the surface of filter 114 is scraped by face 111 toremove ice which has been drawn to and adhered to filter 114.

FIG. 5 shows a second embodiment of a separator suitable for use withthe system of FIG. 1. In this arrangement, a conically shaped convergingscrew 160 is used to compact the slurry which enters vessel 162 at inlet164. Screw conveyor 160 is rotated continually by a motor (not shown)with the speed of rotation determining the output of the separator. Incontrast to the arrangement of FIGS. 2-4, this embodiment operatescontinuously so that the output does not periodically increase nordecrease. Filter 166 through which the liquid is forced by the conicallyconverging screw 160 is also formed as shown in FIG. 4. The liquidforced through filter 166 leaves through outlet 168, while the iceslurry leaves through outlet 170. Liquid entering through inlet 171 fromthe stage to which the ice is to be passed and scraper 172 slurries theice which has been compacted and makes its movement to the next stageeasier.

Another possible separator which can be used is a wash column with thetop flushed with lower concentrate rather than wash water.

Reference is now made to FIG. 6 which illustrates a further embodimentof the counter-current system of the present invention. As in theprevious embodiment, a feed to be concentrated is supplied to a tank 200where it is mixed with liquid from a wash column 202 and supplied to aplurality of scraped surface heat exchanger 204, 206, 208 and 210 viatank 212. Pump 214 moves the liquid in tank 200 into intermediate tank212. The scraped heat exchangers supply their output to recrystallizingvessel 216, and the liquid removed threfrom via filter 218 is partiallyrecirculated by pumps 220, 222, 224 and 226 and partially supplied as anintermediate concentrated liquid to a second stage includingrecrystallizing vessel 230, heat exchangers 232, 234 and 236 and pumps238, 240 and 242. The liquid withdrawn from recrystallizing vessel 230through filter 243 similarly is partially recirculated and partiallypassed to a third stage including recrystallizing vessel 244, heatexchangers 246 and 248 and pumps 250 and 252. The final concentratedproduct is rmoved from the recrystallizing vessel via filter 254, and apart thereof is recirculated as in the other stages.

The embodiment of FIG. 6 includes a pair of separators 260 and 262 whichfunction as in the above-described embodiment to replace a part of theliquid from the ice slurry with the liquid from the stage to which it isto be supplied and pass the ice to the preceding stage incounter-current fashion. FIG. 7 shows the embodiment of a separatorwhich will carry out these functions. FIG. 8 shows a preferredembodiment of the separator 260 and 262 to remove as much liquid fromthe ice slurry from the preceding stage as possible and replace withliquid from the stage to which it is to be supplied.

Referring again to FIG. 6, liquid withdrawn from recrystallizer vessel216 is positively pumped by a positive displacement pump 322 toseparator 260 and the liquid which is withdrawn through filter 316 (seealso FIG. 6) positively pumped to the second stage by pump 324. Since inthe systems of FIGS. 1 and 6 the vessels are always full, withdrawal ofa given volume of liquid at a given rate from one vessel requires thatan equal amount of replacement liquid be withdrawn from another vesselat the same rate. Thus, the amount of liquid which is returned to vessel230 by pump 324 minus the product flow rate is identical to the amountof liquid mixed with the slurry of ice supplied to separator 260.

FIG. 7 shows a first embodiment of such a separator using a conventionalrecrystallizer for that purpose. In the recrystallizer vessel 304, anagitator 306 is continually rotated to move upward slurry receivedthrough inlet 308 which slurry moves over the top of draught tube 310and is eventually removed through outlet 312. Liquid is continuouslywithdrawn through outlet 314 via conventional filter 316. A scrapingknife 318 continually removes ice which builds up on the outside offilter 316 and that ice is blown upward by liquid from the stage towhich ice is to be transported and circulated by the agitator 306. Theliquid from the stage to which the ice is to be transported is suppliedvia inlet 320.

FIG. 8 shows a separator which can be used with the second embodiment ofthe present invention. In this separator, the slurry is supplied to agenerally cylindrical tank 348 by inlet 350 and the liquid is withdrawnby a positive displacement pump through filter 352 which is of the typedescribed above. Filter 352 is continually rotated by a motor and theice which cakes on the outside of filter 352 is scraped from theexterior surface of filter 352 by a blade 354 mounted on member 356. Lowconcentrated liquid from the stage to which the ice is to be supplied isblown by a positive displacement pump into the unit tangentially to theaxis of rotation at inlet 360 to cause the ice to be slurried and passedas a slurry from outlet 362 to the preceding stage. The low concentratealso penetrates to some extent through the filter and mixes with thehigher concentrated solution so that the separator functions not only tomove the ice but also to move the liquid in the opposite directiontoward the next stage for further concentration to realize thecoutercurrent fashion. The mixed low concentrate and high concentrateliquid pass through apertures in the central cylinder 370 and areremoved at outlet 374.

It is not necessary that the slurry supply line be radial. A long filtercan be used and the slurry supply line made tangential with an insidepipe having a long opening. The discharge line and the injection inletis also preferably tangential, but can be made axially mounted ifdesired.

It is also possible that an open connection can simply be providedbetween the recrystallizer vessels and between the stages with apositive displacement pump taking liquid of a preceding stage to thenext stage compensating the production and the counter-current flow ofslurry. No intermediate tanks are needed with this arrangement, but thisapproach is inefficient in that too much concentrated liquid moves withthe ice to the previous stage, and as a consequence, the concentrationdifference between each stage is less than desired. The use of any opentanks in a system which concentrates liquid such as coffee and the likeis undesirable since the open vessels lead to the loss of dissolvedgases and aroma components.

The following Example 1 sets forth the parameters for operation of thefirst embodiment of the invention; and the following Example 2, foroperation of the second embodiment.

    ______________________________________                                                 Amount of   Concentration                                                                              Amount of                                   No.      liquid (kg/h)                                                                             (wt %)       ice (kg/h)                                  ______________________________________                                        1        8,475       29.3         --                                          2        2,949       29.3         --                                          3        4,974       22.4         --                                          4        9,715       28.1         785                                         5        3,000       29.3         1,500                                       6        3,000       29.3         --                                          7        1,500       0.0          --                                          8        1,650       38.1         825                                         9        5,725       38.1         --                                          10       1,674       38.1         --                                          11       6,465       37.2         535                                         12         800       50.0         400                                         13       5,800       50.0         --                                          14       6,445       51.2         555                                         F = feedrate                                                                           1,974       12           --                                          P = product-                                                                  rate     474         50           --                                          W = water                                                                     removal                                                                       rate     1,500       0            --                                          Plant consists of: three washcolumns + first stage, second stage,             third stage                                                                   Volume recrystallizer vessels: 2,850 liters.                                  ______________________________________                                        Recrystallizer                                                                              Temperature                                                                              Deff (micron)                                        ______________________________________                                        First stage   -4.1° C.                                                                          219                                                  Second stage  -6.0° C.                                                                          180                                                  Third stage   -9.6° C.                                                                          141                                                  ______________________________________                                         Residence time S.S.H.E.: 0.2 min.                                             Deff.: 5 microns                                                         

    ______________________________________                                                  Amount of   Concentration                                                                             Amount of                                   No.       liquid (kg/h)                                                                             (wt %)      ice (kg/h)                                  ______________________________________                                        1         11,210      23.1        --                                          2         4,173       23.1        --                                          3         6,963       18.7        --                                          4         12,940      22.6        1,060                                       5         4,200       23.1        2,100                                       6         4,200       23.1        --                                          7         2,340       27.1        1,170                                       8         2,340       34.2        1,170                                       9         4,173       27.1        --                                          10        8,265       34.2        --                                          11        1,938       34.2        --                                          12        9,640       34.2          860                                       13          850       39.0          425                                       14          850       50.0          425                                       15        1,938       39.0        --                                          16        5,725       50.0        --                                          17        6,445       51.0          555                                       F = feedrate                                                                            2,763       12.0        --                                          P = product-                                                                  rate        663       50.0        --                                          W = water                                                                     removal                                                                       rate      2,100        0.0        --                                          Plant consists of: four washcolumns + first stage, second stage,              third stage.                                                                  Volume recrystallizer vessels: 2,850 liters.                                  ______________________________________                                        Recrystallizer                                                                              Temperature Deff. (microns)                                     ______________________________________                                        First stage   -3.1° C.                                                                           230                                                 Second stage  -5.0° C.                                                                           189                                                 Third stage   -9.6° C.                                                                           135                                                 ______________________________________                                         Residence time S.S.H.E.: 0.2 min.                                             Deff.: 5 microns                                                         

Many changes and modifications in the above embodiments can, of course,be carried out without departing from the scope of the invention. Thatscope is intended, therefore, to be limited only by the scope of theappended claims.

What is claimed is:
 1. A multiple-stage, counter-current system forconcentrating an aqueous feed liquid to produce a concentrated productcomprising:a first concentrating stage for receiving said feed liquidand producing an intermediate concentrated liquid including first seedcrystal forming means for receiving feed liquid and forming a slurry ofseed ice crystals and feed liquid, first recrystallizing means forreceiving said slurry from said first seed crystal forming means andproducing a first slurry containing larger crystals, first means forseparating a portion of the liquid from crystals from said firstrecrystallizing means and supplying at least part of said portion tosaid first seed crystal forming means, and first means for removing saidslurry from said first recrystallizing means and separating the largercrystals removed from said recrystallizing means; at least a secondconcentrating stage for receiving said intermediate liquid and producingsaid concentrated product including second seed crystal forming meansfor receiving said intermediate liquid and forming a slurry of seed icecrystals and intermediate liquid, second recrystallizing means forreceiving said slurry from said second seed crystal forming means andproducing a second slurry containing larger crystals, second means forseparating a portion of the liquid from crystals from said secondrecrystallizing means and supplying at least part of said portion tosaid second seed crystal forming means, and means for removing saidsecond slurry from said second recrystallizing means; and means forsupplying at least said larger crystals removed from said secondrecrystallizing means to said first recrystallizing means so that atleast substantially all of the seed crystals in said firstrecrystallizing means melt and reform on said larger crystals from saidsecond recrystallizing means.
 2. A system as in claim 1, wherein saidfirst means for removing and separating includes at least one washcolumn.
 3. A system as in claim 1 or 2 wherein said first and secondportion separating means each include a filter in the recrystallizingmeans.
 4. A system as in claim 1 or 2, wherein said first and secondseed crystal forming means each include at least one scraped surfaceheat exchanger.
 5. A system as in claim 1 or 2, further including athird concentrating stage for receiving said concentrated liquid fromsaid second stage and producing a further concentrated product includingthird seed crystal forming means for receiving said concentrated liquidfrom said second stage and forming a slurry of seed ice crystals andsaid concentrated liquid, third recrystallizing means for receiving saidslurry from said third seed crystal forming means and producing a thirdslurry containing larger crystals, third means for separating a portionof the liquid from crystals in said third recrystallizing means andsupplying said portion to said third seed crystal forming means, meansfor removing said slurry from said third recrystallizing means and meansfor supplying at least said larger crystals removed from said thirdrecrystallizing means to said second recrystallizing means so that theseed crystals in said second recrystallizing means melt and reform onsaid larger crystals from said third recrystalling means.
 6. A system asin claim 1 or 2, further including means for mixing said feed liquidwith the liquid separated from the larger crystals in said firstremoving and separating means to produce a first mixed liquid, and meansfor supplying said first mixed liquid to said first seed crystal formingmeans.
 7. A system as in claim 1 or 2, further including means forsupplying the remainder of said portion separated from said firstrecrystallizing means to said second seed crystal forming means as saidintermediate concentrated liquid.
 8. A multiple-stage, counter-current,freeze concentration system for concentrating an aqueous feed liquid toproduce a concentrated product comprising:a first stage including:(a) atleast one scraped surface heat exchanger for producing continuously aslurry of said feed liquid and seed crystals of an effective diameterless than 10 microns; (b) recrystallizing means including arecrystallization vessel connected to said heat exchangers of said firststage for continuously receiving said slurry and growing crystals toform a slurry with crystals larger than said seed crystals; (c) meansfor removing a portion of the liquid within said vessel of said firststage and recirculating a part of the portion to the heat exchanger ofsaid first stage; (d) at least one wash column for receiving said slurryfrom said vessel of said first stage and separating the ice and liquid;(e) means for mixing the liquid separated by said wash column of saidfirst stage with said feed liquid and supplying the mixture to said heatexchanger of said first stage; and (f) means for withdrawing the liquidin said vessel of said first stage as an intermediate concentratedproduct; and a second stage including:(a) at least one scraped surfaceheat exchanger for producing a slurry of said intermediate product andseed crystals of an effective diameter of less than 10 microns; (b)recrystallizing means including a recrystallization vessel connected tosaid heat exchangers of said second stage for continuously receivingsaid slurry and growing crystals to form a second slurry with crystalslarger than said seed crystals; (c) means for removing a portion of theliquid within said vessel of said second stage and recirculating a partof the portion to the heat exchanger of said second stage; (d) means forremoving said second slurry from said vessel of said second stage; (e)means for supplying at least the ice crystals in the second slurry tothe vessel of said first stage so that at least substantially all of theseed crystals in said vessel of said first stage melt and reform on thecrystals from said second stage; and (f) means for withdrawing theliquid in said vessel of said second stage as said concentrated product.9. A system as in claim 1 or 8, wherein said supplying means includesmeans for removing at least part of the liquid from said second slurrybefore supplying said larger crystals to said first recrystallizingmeans.
 10. A system as in claim 9, wherein said removing means includesa vessel having an interior space with an inlet for receiving saidsecond slurry, first and second outlets and a valve associated with eachinlet and outlet for controlling flow therethrough, a pistonreciprocable in said space to compact said second slurry, filter meansdisposed in said space so that liquid from said second slurry passestherethrough to said first outlet when said piston is reciprocated whilepreventing passage of said ice so as to compact said ice which thenmoves out said second outlet, means for reciprocating said piston andcontrol means connected to said valves and said reciprocating means forcyclically operating the same to remove some of the liquid from saidsecond slurry.
 11. A system as in claim 10 wherein said filter meansincludes a cylindrical filter having a plurality of triangular shapedwires fixed to a plurality of encircling bands to form slots throughwhich liquid can move but ice is excluded, said filter being mounted sothat the surface is scraped by said reciprocating piston.
 12. A systemas in claim 11, including scraping means adjacent said first outlet forscraping ice from said filter means.
 13. A system as in claim 10,wherein said removing means includes a vessel having an interior spacewith an inlet for receiving said second slurry, an inlet for receivingliquid from said first stage to slurry ice removed from said secondslurry, and first and second outlets, a conically converging screwconveyor for transporting and compacting said second slurry, duringmovement toward said first outlet at which ice slurried with liquid fromsaid first stage is removed, and filter means disposed in said space sothat liquid from said second slurry passes therethrough to said secondoutlet while preventing passage of said ice so as to compact said ice.14. A system as in claim 9, wherein said removing means includes avessel having an interior space with an inlet thereto for receiving saidsecond slurry, a first outlet for liquid removed from said second slurryand a second outlet for a slurry including said larger crystals, meansfor transporting said second slurry toward said second outlet, andfilter means disposed in said space adjacent the path of travel of saidsecond slurry so that liquid from said second slurry passes therethroughto said first outlet while preventing passage of ice therethrough.
 15. Asystem as in claim 9, wherein said supplying means includes means forremoving at least a portion of liquid from said second slurry, returningthe removed portion to said second stage, adding liquid from said firststage to said second slurry, and supplying the resultant slurry to saidfirst stage.
 16. A system as in claim 15, wherein said supplying meansfurther includes a first pump means for pumping liquid from said firststage to said removing means at a given rate and a second pump means forpumping liquid from said removing means to said second stage at a givenrate.
 17. A system as in claim 16 wherein said removing means includes avessel having an interior space with a first inlet for receiving saidsecond slurry, a second inlet for receiving liquid from said first stageto slurry ice removed from said second slurry and first and secondoutlets, agitator means for transporting slurry from said first inlettoward said first outlet, at which slurry is removed and filter meansdisposed in said space so that liquid from said second slurry passestherethrough to said second outlet while preventing passage of said ice.18. A system as in claim 12 wherein, said agitator means moves slurryupward and over the top of a draught tube to said first outlet, and saidremoving means further includes means for continuously scraping saidfilter means, said second inlet being arranged to blow ice scraped fromsaid filter means upward.
 19. A system as in claim 15 wherein saidremoving means includes a vessel having an interior space with a firstinlet for receiving said second slurry, a second inlet for receivingliquid from said first stage to slurry ice removed from said secondslurry and first and second outlets, agitator means for transportingslurry from said first inlet toward said first outlet, at which slurryis removed and filter means disposed in said space so that liquid fromsaid second slurry passes therethrough to said second outlet whilepreventing passage of said ice.
 20. A system as in claim 19 wherein,said agitator means moves slurry upward and over the top of a draughttube to said first outlet, and said removing means further includesmeans for continuously scraping said filter means, said second inletbeing arranged to blow ice scraped from said filter means upward.
 21. Asystem as in claim 15 or 16 wherein said removing means includes avessel having an interior space with a first inlet for receiving saidsecond slurry, a second inlet for receiving liquid from said first stageto slurry ice removed from said second slurry and first and secondoutlets, a rotatable filter disposed radially inwardly from said firstinlet so that liquid passes therethrough to said first outlet while iceis caked on said filter and transported toward said second outlet andmeans for scraping said ice from said filter so that said ice isslurried with liquid from said second inlet.
 22. A system as in claim 9,wherein said removing means includes a vessel having an interior space,an inlet for supplying a slurry of ice and liquid from therecrystallizng means of the succeeding stage to said space, meansmounted for movement in space for compacting said slurry, a filtermounted adjacent said compacting means so that liquid is forced throughsaid filter by said compacting means while said ice does not passthrough said filter, a first outlet for receiving said liquid forcedthrough said filter for return to said succeeding stage and a secondoutlet for receiving the compacted ice for passage to therecrystallizing means of the preceding stage.
 23. A system as in claim8, wherein said first and second stage each include at least two heatexchangers connected in parallel to each other.
 24. A system as in claim8 or 23, wherein said removing and recirculating means of said first andsecond stages each include a filter.
 25. A system as in claim 8 or 23,wherein said second stage includes means for separating the ice andliquid from the slurry removed from said vessel of said second stage andmixing the separated liquid with said intermediate product.
 26. A systemas in claim 8, further including:a third stage including:(a) at leastone scraped surface heat exchanger for producing a slurry of saidintermediate product and seed crystals of an effective diameter of lessthan 10 microns; (b) a recrystallization vessel connected to said heatexchangers of said third stage for continuously receiving said slurryand growing crystals to form a slurry with crystals larger than saidseed crystals; (c) means for removing a portion of the liquid withinsaid vessel of said third stage and recirculating a part of the portionof the heat exchanger of said third stage; (d) means for removing saidslurry from said vessel of said third stage and supplying at least theice crystals in the slurry to the vessel of said second stage so thatthe seed crystals in said vessel of said second stage melt and reform onthe crystals from said third stage; and (e) means for withdrawing theliquid in said vessel of said third stage as said concentrated product.27. A method of concentrating an aqueous beverage feed liquid to producea concentrated product comprising:forming a first slurry of seed icecrystals and liquid including said feed liquid; supplying said firstslurry to a first recrystallization vessel to grow larger crystalstherein; separating a portion of the liquid in said first vessel fromthe larger crystals therein and adding at least a part of the separatedliquid to said first feed liquid; removing said slurry with said largercrystals from said recrystallization vessel and separating the largercrystals in the slurry from the liquid; removing a portion of the liquidfrom said first vessel and adding at least a part thereof to said feedliquid before forming said first slurry of seed crystals; forming asecond slurry of seed ice crystals and liquid from said first vessel;supplying said second slurry to a second recrystallization vessel togrow larger crystals therein; removing a portion of the liquid from saidsecond vessel and adding at least a part thereof to liquid from saidfirst vessel before forming said second slurry; and supplying the largercrystals from said second vessel to said first vessel so that at leastsubstantially all said seed crystals therein melt and reform on saidlarger crystals from said second vessel.
 28. A method as in claim 27,wherein said liquid is chosen from the group consisting of fruit juices,milk, beer, wine, vinegar, tea and coffee.
 29. A method as in claim 27,wherein said step of forming a slurry includes the step of supplyingliquid including feed liquid to at least one scraped surface heatexchanger.
 30. A method as in claim 27, wherein said step of separatingincludes supplying said slurry with said larger crystals to a washcolumn.
 31. A method as in claim 27, including the further steps ofseparating the ice and liquid from said second vessel and mixing theseparated liquid with the liquid from said first vessel before formingsaid second slurry.
 32. A method as in claim 27, including the furthersteps of:forming a third slurry of seed ice crystals and liquid fromsaid second vessel; supplying said third slurry to a thirdrecrystallization vessel to grow larger crystals therein; removing aportion of the liquid from said third vessel and adding at least a partthereof to liquid from said second vessel before forming said thirdslurry; and supplying the larger crystals from said third vessel to saidsecond vessel so that said seed crystals therein melt and reform on saidlarger crystals from said third vessel.